Overview of Biochemistry I Topics

This study guide summarizes the foundational topics in a college-level Biochemistry I course, focusing on the structure and function of biomolecules, the chemistry of water and pH, protein structure, and enzyme kinetics and regulation.

Cells and Biomolecules

Cells

Cells are the basic structural and functional units of life. They can be classified as prokaryotic (lacking a nucleus) or eukaryotic (with a nucleus and organelles).

• Prokaryotic cells: Simpler, no membrane-bound organelles, e.g., Escherichia coli.

• Eukaryotic cells: Complex, contain nucleus and organelles, e.g., animal and plant cells.

Biomolecules and Biological Macromolecules

Biomolecules are organic molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Energy storage and structural roles.

• Lipids: Membrane structure, energy storage, signaling.

• Proteins: Catalysis (enzymes), structure, transport, signaling.

• Nucleic acids: Genetic information storage and transfer (DNA, RNA).

Water and pH

Water: The Medium of Life

Water is the most abundant molecule in cells and is essential for biochemical reactions due to its polarity and hydrogen bonding capacity.

• Polarity: Allows water to dissolve many ionic and polar substances.

• Hydrogen bonding: Leads to high specific heat, cohesion, and surface tension.

pH and the Henderson-Hasselbalch Equation

pH measures the hydrogen ion concentration in a solution, influencing enzyme activity and molecular structure.

• pH definition:

• Henderson-Hasselbalch equation: Relates pH, pKa, and the ratio of conjugate base to acid.

Titration Curves

Titration curves show how the pH of a solution changes as acid or base is added, useful for determining pKa values of weak acids and bases.

• Buffer region: Area where pH changes slowly upon addition of acid/base.

• Equivalence point: Point where acid is completely neutralized.

Amino Acids and Protein Structure

Amino Acids

Amino acids are the building blocks of proteins, each containing an amino group, carboxyl group, hydrogen atom, and unique side chain (R group) attached to a central carbon.

• Classification: Nonpolar, polar uncharged, acidic, and basic amino acids.

• Essential amino acids: Cannot be synthesized by the body and must be obtained from diet.

Reactions of Amino Acids and the Peptide Bond

Amino acids link via peptide bonds to form polypeptides and proteins.

• Peptide bond: Covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water.

• Reaction: Condensation (dehydration synthesis).

Chirality of Amino Acids

All amino acids (except glycine) are chiral, existing as L- and D- isomers. Proteins are composed exclusively of L-amino acids.

Primary Sequence of Amino Acids

The primary structure of a protein is its unique sequence of amino acids, determining its final 3D structure and function.

Experimental Methods for Protein Sequencing

• Edman degradation: Sequentially removes and identifies N-terminal amino acids.

• Mass spectrometry: Determines mass and sequence of peptides.

Secondary Structure of Proteins

Secondary structure refers to local folding patterns stabilized by hydrogen bonds.

• Alpha helix: Right-handed coil stabilized by hydrogen bonds.

• Beta sheet: Sheet-like arrangement, can be parallel or antiparallel.

Protein Folding and Higher-Order Structure

Protein Folding

Protein folding is the process by which a polypeptide chain acquires its biologically active 3D structure.

• Folding driven by: Hydrophobic interactions, hydrogen bonds, van der Waals forces, and disulfide bonds.

• Chaperones: Proteins that assist in folding.

Tertiary and Quaternary Structure

• Tertiary structure: Overall 3D shape of a single polypeptide chain.

• Quaternary structure: Association of multiple polypeptide chains (subunits) into a functional protein complex.

Enzyme Kinetics and Regulation

Kinetics of Enzyme-Catalyzed Reactions

Enzyme kinetics studies the rates of enzyme-catalyzed reactions and how they change in response to changes in substrate concentration and other factors.

• Michaelis-Menten equation:

• Vmax: Maximum reaction velocity.

• Km: Substrate concentration at half-maximal velocity.

Enzyme Inhibition

Enzyme inhibitors decrease enzyme activity. Types include:

• Competitive inhibition: Inhibitor binds active site; increases Km, Vmax unchanged.

• Noncompetitive inhibition: Inhibitor binds elsewhere; decreases Vmax, Km unchanged.

• Uncompetitive inhibition: Inhibitor binds only to enzyme-substrate complex; decreases both Vmax and Km.

Mechanisms of Enzyme Action

Enzymes lower activation energy and increase reaction rates by stabilizing the transition state.

• Mechanisms: Acid-base catalysis, covalent catalysis, metal ion catalysis, proximity and orientation effects.

Regulation of Enzyme Activity

Enzyme activity is regulated to meet cellular needs.

• Allosteric regulation: Effector molecules bind sites other than the active site, altering activity.

• Covalent modification: Phosphorylation, acetylation, etc.

• Proteolytic activation: Activation by cleavage of peptide bonds.

Summary Table: Weekly Topics